Question

A manufacturing company wants to develop control charts to measure the quality of its steel plate. They take ten sheets of 1" steel plate and compute the number of cosmetic flaws on each roll. Each sheet is 20' by 100'. Based on the following data.

Sheet	1	2	3	4	5	6	7	8	9	10
# of flaws	1	1	2	0	1	5	0	2	0	2

a. Compute the lower control (LCL) limit

b. Compute the upper control (UCL) limit

c. Is the process under control ?

Answer 1

Question: A manufacturing company wants to develop control charts to measure the quality of its steel plate. They take ten sheets of 1" steel plate and compute the number of cosmetic flaws on each roll. Each sheet is 20' by 100'. Based on the following data.

Answer:

From given data:

Total number of sheets = 10

Total number of flaws = 14

Therefore:

Using c-chart, centerline is given by:

Centerline (c) = Total number of flaws / Total number of sheets

Therefore:

Centerline (c) = 14 / 10

Centerline (c) = 1.4

a. Compute the lower control (LCL) limit

Lower Control Limit (LCLc) is given by:

LCL = c - 3 x Sqrt(c)

Therefore:

LCL = 1.4 - 3 x Sqrt(1.4)

LCL = -2.14964786986

LCL = 0

b. Compute the upper control (UCL) limit

Upper Control Limit (UCLc) is given by:

UCL = c + 3 x Sqrt(c)

Therefore:

UCL = 1.4 + 3 x Sqrt(1.4)

UCL = 4.94964786986

UCL = 4.949648

c. Is the process under control ?

Here:

Sample 6 = 5

UCL = 4.949648

Therefore:

Sample 6 is above the control limits hence the process is out of control.